Remove an unused function

The function is a leftover before API cleanup.
Fix a possible invalid read and write.

It is possible that authentication request survived EnginioClient
destruction. In such case finished signal triggering
SessionSetterFunctor was causing an invalid read and write to already
deleted EnginioClientPrivate.
Introduce authenticationState property in EnginioClient.

During API we agreed that isAuthenticated bool is not good enough, for
example it is not trivial to have a spinning icon during login phase,
without tracking right signals.

The enum structure is not final yet and I'm sure we should have another
round of review for it.
Emit sessionAuthenticated together with EnginioReply

The signal is replacement for removed identityToken.
New tests for identity check

Setting identity should reset the sessionToken, which is part of a
QNetworkRequest header.
Add missing const to EnginioClient::networkManager accessor.
Use "Q_SIGNALS" instead of "signals"
Fix signuture of authenticationStateChange signal

AuthenticationState is an enum reference is not needed.
Fix warning about initialization order.
Add an argument to EnginioReply::finished signal
Remove ignore SSL errors hack.
Fix a memory leak

EnginioReplyPrivate don't have virtual destructor, we need to
manually call the right destructor
Merge pull request #91 from nierob/changesAfterFirstAndSecondReviewAndSmallImprovements

Changes after first and second review and small improvements